geometry : Wrapping a gift

Your question is essentially asking for the surface area of the box, because you are looking for the amount of material to cover the surface of the box. This can be done by summing up the area of each side of the box or by following the formula below

Surface area = 2ab + 2ac + 2bc

where a, b and c are the length of each side of the box.

Using the given dimensions we can find the surface area

Surface area = 2*18*16 + 2*18*4 + 2*16*4

Surface area = 576 + 144 + 128

Surface area = 848 in^2

This corresponds to answer (3).

If you have any additional questions about this, please do not hesitate to ask.